There has been developed a solid electrolytic capacitor obtained by forming a dielectric oxide film on a porous body of a valve-acting metal such as tantalum or aluminum by anodic oxidation and then forming on the oxide film a conductive polymer layer as a solid electrolyte. Roughly classified, there are chemical oxidation polymerization and electrolytic oxidation polymerization as methods for forming the conductive polymer layer of the solid electrolytic capacitor. As a monomer forming a conductive polymer material, there are known pyrrole, thiophene, 3,4-ethylene dioxythiophene, aniline, and so on.
Such a solid electrolytic capacitor has a lower equivalent series resistance (hereinafter referred to as “ESR”) as compared with a conventional capacitor using manganese dioxide as a solid electrolyte and thus has started to be used in various applications. In recent years, following the trend toward higher frequencies and larger currents of integrated circuits, there have been demanded solid electrolytic capacitors with low ESR, large capacitance, and small loss.
Techniques relating to such solid electrolytic capacitors are disclosed in Patent Document 1 (Japanese Unexamined Patent Application Publication (JP-A) No. 2000-232036) and Patent Document 2 (Japanese Unexamined Patent Application Publication (JP-A) No. 2003-229330).
Patent Document 1 achieves a low ESR by mixing conductive particles having plasticity or flexibility into a conductive polymer layer to provide irregularities at the interface of the conductive polymer layer with a cathode conductor layer, thereby increasing the contact area between the conductive polymer layer and the cathode conductor layer.
Patent Document 2 proposes a solid electrolytic capacitor manufacturing method characterized by comprising a step of forming a first conductive polymer film serving as part of a conductive polymer layer in a first solution and a step of forming a second conductive polymer film serving as another part of the conductive polymer layer in a second solution having a pH lower than that of the first solution, wherein the first conductive polymer film and the second conductive polymer film are both formed by electrolytic oxidation polymerization, thereby achieving a low ESR and an increase in capacitance.